(a) Technical Field
The present invention relates to a manifold block for a fuel cell stack. More particularly, it relates to a manifold block for a fuel cell stack, which can guarantee excellent electric insulation of a cooling water passage disposed within internal passages of the manifold block, the cooling water passage having a straight-line shape that is bent at a certain angle.
(b) Background Art
A fuel cell is a type of power generation device that converts chemical energy of fuel into electrical energy by an electrochemical reaction in a stack, instead of transforming the chemical energy into heat by combustion. Among the various types of fuel cells, Polymer Electrolyte Membrane Fuel Cells (PEMFCs, also known as Proton Exchange Membrane Fuel Cells) having a high power density are being extensively studied as a power supply source for driving vehicles.
Polymer electrolyte membrane fuel cells include a Membrane-Electrode Assembly (MEA) formed of (a) a solid polymer electrolyte membrane through which hydrogen ions move, (b) catalyst electrode layers, in which an electrochemical reaction occurs, attached to both surfaces of the solid polymer electrolyte membrane, (c) a gas diffusion layer, that evenly distributes reactant gases and serves to transmit generated electrical energy, provided on the outer sides of each catalyst electrode layer, and (e) a gasket and coupling members for maintaining appropriate pressure and for maintaining air-tightness to prevent leakage of reactant gases and cooling water. A bipolar plate that allows reactant gases and cooling water to move along a reaction passage is further stacked on the outer sides of the gas diffusion layers to form a unit fuel cell. A fuel cell stack having a desired power output is then manufactured by stacking a plurality of such unit cells.
Further, a manifold block is assembled into the fuel cell stack. The manifold block is a kind of passage member that allows gases and cooling water to flow into and out of a fuel cell before and after a reaction, and forms an inlet passage and an outlet passage of a fuel cell stack.
The manifold block has a long and complicated internal passage that allows gases and cooling water to pass through. When a plurality of stack modules are mounted in a fuel cell vehicle, a manifold block attached to the outer side of the stack module serves to evenly supply reactant gases (air and hydrogen) and cooling water to each stack module.
In order to manufacture such a manifold block, a method is provided wherein a block shape is formed using an aluminum casting process, followed by coating cooling water passages with insulation.
FIG. 1 is a cross-sectional view illustrating a typical manifold block having a cooling water passage 11 and coupled to a stack module, which is taken along the cooling water passage 11.
As shown in FIG. 1, an end plate 31 is coupled to the outmost side of a stack module 30 in which unit cells, such as membrane-electrode assembly, gas diffusion layer, bipolar plate and gasket are stacked, and a manifold block 10 is attached to the outer side of the end plate 31 with a gasket 32 is disposed therebetween.
An interface part 14 for receiving cooling water is coupled to one side of the manifold block 10. Cooling water supplied to the interface part 14 passes through the cooling water passage 11 in the manifold block, and is then supplied to the stack module 30. Cooling water from the stack module 30 is subsequently exhausted to the outside via a further interface part (not shown). In particular, cooling water from the stack module 30 passes through a further cooling passage (not shown), and the further interface part for exhausting the cooling water from the stack module 30.
The interface part 14 and further interface part may be formed of a suitable insulating material, such as plastic and the like.
As shown, the cooling water passage 11 is bent at a certain angle and has a straight-line shape in the manifold block 10. During operation of the fuel cell stack, the cooling water passage 11 is always full of cooling water.
Thus, while cooling water is contained in the cooling water passage 11 of the manifold block 10, high-voltage electricity generated in the stack module 30 may leak out through cooling water. Such leakage of electricity may cause electric shock to a user or a worker.
Accordingly, in order to prevent leakage of electricity, an insulation coating (e.g., ceramic coating, epoxy coating, and Teflon coating) is provided on the entire cooling water passage 11 of the manifold block 10.
However, while the manifold block 10 shown in FIG. 1 is advantageous because a differential pressure can be reduced due to the simple structure and a sufficient size of a cooling water passage, it also presents limitations in coating. In particular, the manifold block 10 has limitations in that significant deviation of coating quality occurs according to working conditions during the insulation coating process, and the surface roughness increases due to lumping of the coating.
Also, although insulation performance may be satisfactory initially, as time goes by, deterioration of the coating progresses and the insulation coating is gradually reduced. Furthermore, electrical corrosion occurs as the insulation coating deteriorates.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.